1. Field of the Invention
The present invention relates to a process for producing a molded article having a hollow portion from a molten charge comprising at least one thermoplastic resin.
2. Description of the Related Art
As a process for producing a hollow article, Japanese Patent Examined Publication No. Shou 57-14968 discloses supplying a molten resin into a closed mold cavity, the amount of the molten resin not being sufficient to fill the mold cavity, and then supplying a compressed gas or a combination of a compressed gas and an additional amount of molten resin into the mold cavity. This related art process, however, is disadvantageous insofar as the resulting hollow molded article has surfaces that exhibit hesitation marks or switching marks (i.e., an unevenness of luster), which are caused by changes in pressure applied to the molten resin while the molten resin is spreading in the cavity.
Japanese Patent Examined Publication No. Hei 7-315 discloses a process wherein a mold cavity is filled with a molten resin and then compressed gas is fed into the molten resin. This latter process, however, is also plagued with problems. For example, assistant equipment, such as a slidable core which is movable in t he mold cavity and the like, is required in order to increase a volume of the mold cavity to form a hollow portion. Tooling having such assistance equipment is often quite expensive and requires high maintenance.
A need therefore exists to provide a process for producing a hollow molded article in which the resulting hollow molded article has a good surface appearance without any hesitation marks, and a process in which expensive and high-maintenance assistant equipment is not required.